Polymerase chain reaction (PCR) technology permits nucleic acid material, such as DNA, often extracted from as little as a single cell, to be amplified to hundreds of millions of copies. This is important since prior to PCR technology it was virtually impossible to detect a single DNA strand. However, when a single DNA strand, such as the DNA produced by a human immunodeficiency virus (e.g., HIV-I, otherwise known to cause AIDS), is added to amplifying reagents that will amplify the DNA of choice, hundreds of millions of copies of that DNA can be obtained in a relatively short time. Technology further allows for the detection of the amplified nucleic acid material (DNA for example), using probes that hybridize to the amplified material of choice, such probes in turn either being immobilized or immobilizable to a solid support, such as a filter membrane, and/or being labeled for detection using enzymes or other moieties.
Conventionally, this has been done by amplifying the nucleic acid material in a stoppered plastic container until the desired number of copies have been formed. Thereafter, the container is reopened, such as by unstoppering, and either the amplified copies are withdrawn and transferred to detection apparatus, or detecting reagents are added to the container used for the amplification, so that detection is done in the same container.
It has been discovered that such a technique is unsatisfactory for convenient and widespread use of PCR technology, because aerosols are produced in the act of unstoppering and/or transfer of fluids. Such aerosols contain a few molecules of the amplified nucleic acid material, e.g., DNA. The aerosols then proceed to disperse within the environment. Normally, such few molecules in the environment are not of great concern. However, in theory, only one DNA molecule is needed to ruin by contamination other amplifying containers yet to be used for detection. That is, if the errant DNA molecule floats into or is carried, inadvertently, by an operator to another amplifying container yet to be used, that one molecule is all that is needed to provide the DNA needed for the next amplification. Needless to say, if the point of the next test is to see if a particular DNA is present (e.g., from HIV-I), and it is detected only because of the errant DNA and not that of the patient, the test is ruined. Thus, the very power of DNA amplification becomes the source of potential ruin of the tests. As a matter of fact, an entire lab has been proven to be contaminated by the unstoppering of just a few containers in which the sample has already been amplified. Although such a problem might be avoidable by using highly skilled and trained personnel who painstakingly minimize the aerosols produced, the need for such labor makes the technology impractical for general use.
The aforesaid problem has been solved by a containment cuvette, which as described and claimed in commonly-owned U.S. application Ser. No. 306,735 filed on Feb. 3, 1989, entitled "Containment Cuvette for PCR and Method of Use", can be a flexible pouch. Such pouch features wall materials that define a reaction compartment, one or both of the wall materials in the compartment being flexible.
Although such a pouch can be heated and cooled rapidly by a variety of devices through the numerous temperature changes known in the art to be needed to do PCR amplification, there has been a need prior to this invention for simple, inexpensive and yet efficient temperature control devices especially adapted to such rapid temperature changes. It has been found, for example, that thermal cycling by heating and cooling a metal block on which a pouch sits, is relatively slow and inefficient.